1. Field of the Invention
This invention relates to a magnetic tape cassette. This invention particularly relates to a magnetic tape cassette, which is constituted of a resin and is of a thin-walled type.
2. Description of the Prior Art
Magnetic tape cassettes accommodate hubs, around which magnetic tapes are wound. A magnetic tape cassette has an approximately rectangular bottom wall and a side wall extending along the periphery of the bottom wall. The magnetic tape cassette is integrally molded by feeding a resin from a position corresponding to the vicinity of the center point of the bottom wall into a mold. The bottom wall of the magnetic tape cassette is provided with openings, into which the spindles for rotating the hubs are to be inserted. Also, structural parts for constituting spaces, in which a lock member of a guard panel, and the like, are to be accommodated, are formed at corners of the bottom wall and in proximity to the side wall.
Recently, environmental destruction occurs due to waste plastic materials, or the like. Therefore, for the purposes of reducing the amounts of plastic materials used such that the amounts of waste plastic materials may become small, the thicknesses of magnetic tape cassettes have heretofore been made as small as possible. Specifically, the thicknesses of the bottom wall and the side wall of the magnetic tape cassette, which were approximately 2 mm in the past, are reduced to a range of approximately 1.2 to 1.5 mm.
The amount of the material used can be reduced by making the thicknesses of the bottom wall and the side wall of the magnetic tape cassette small. However, if the thicknesses of the bottom wall and the side wall of the magnetic tape cassette are made small, a resin having been fed into a mold for forming the magnetic tape cassette cannot flow smoothly through the flow path in the mold and will harden before it spreads throughout the mold. Accordingly, the flow path for the resin will be clogged, and the resin is not sufficiently filled in the aforesaid structural parts. Such phenomenon is referred to as "short shot." As a result, a defective magnetic tape cassette is obtained from the molding process.